(Meth)acrylic acid is generally produced by providing (meth)acrylic acid-containing reactant gas produced by gas phase catalytic oxidation reaction into a condensation column or an absorption column to obtain a (meth)acrylic acid aqueous solution, and further purifying the solution. A method in which a (meth)acrylic acid aqueous solution is provided into an azeotropic separation column and azeotropicly distilled in the presence of an azeotropic agent has been widely known as one of such methods for purifying.
However, (meth)acrylic acid is polymerized very easily. Therefore, a polymerization inhibitor is added in a condensation column or an absorption column for inhibiting (meth)acrylic acid from being polymerized.
It is described in Japanese publication of unexamined patent application No. 2001-181252 that manganese acetate may be used as a polymerization inhibitor of (meth)acrylic acid together with an N-oxyl compound. An example in which manganese acetate is dissolved in a feedstock and fed to a distillation column is described in Japanese publication of unexamined patent application No. Hei 5-51403. The feedstock used in the publication is acrylic acid containing 30% by mass of water and 2.5% by mass of acetic acid. An example in which manganese acetate is dissolved in water with other polymerization inhibitors and fed to an azeotropic separation column is described in Japanese publication of unexamined patent application No. 2001-348359. In addition, it is described in Japanese publication of unexamined patent application No. 2004-51489 that a polymerization inhibitor is preferably fed with acrylic acid and manganese acetate is mentioned as one example of polymerization inhibitors.